The invention relates to a system and method for a vertical axis wind turbine (VAWT), which provides a high performance wind turbine design suitable for a range of different power classes such as from 4 kiloWatts to 10 MegaWatts. More particularly, it relates to a system and method for a vertical axis wind turbine, which comprises a single vertical blade and a counterweight, which can overcome the deficiencies of earlier VAWT designs.
In particular, the invention teaches a method, which provides higher efficiency of power generation over a range of wind speeds by using a single blade of chord length C, which is attached to a central hub via a main support strut of chord length C which extends beyond the central hub to connect to a counterweight.
In particular, the invention teaches a method, which provides higher efficiency of power generation over a range of wind speeds by providing a main support strut and two or more control struts, which have differential aerodynamic profiles such that they both strengthen and support the blade and counterweight integrated with the central hub, as well as provide lift and minimise drag.
In essence, the invention makes possible the creation of a new class of high efficiency wind turbines, which can be made of lighter and stronger materials. In particular, the blade, the support strut and the control struts are highly suited to be manufactured as a single element from a single mould thus greatly reducing the cost of manufacture as well as greatly reducing the points of failure of the turbine blade and support struts and control struts. Prior art methods would normally mould the blades and struts separately and connect each strut via separate connections, which adds significant weight to the blade structure thereby reducing its performance.
This patent application relates in part at to an earlier patent application entitled System and Method for Fluid Power Conversion filed 16 Feb. 2010 with application number GB-A-1002558.3 to Philip Wesby and Christopher Turner.
Generally, vertical axis wind turbines (VAWTs) suffer from lower performance when compared to horizontal axis wind turbines (HAWTs) due to their blades not comprising optimised chord lengths and cross sectional profiles. In addition, while VAWTs are always facing the wind whatever the direction of the wind, and can generate power as the wind direction changes, the turning blades move into and out of the wind as they turn, which causes significant stress loads on the turbine blades and support struts, once per revolution.
Consequently, solutions are needed to counter the effect of these cyclical forces.
In prior art VAWT systems the fixing-location where the strut support connects to the blade can suffer extreme fatigue each cycle as the blade moves into and out of the wind direction once per revolution. In particular the point of connection between the blade and strut is prone to failure due to the compressional and tensile forces that are exerted at this point every cycle. Any method, which is capable of mitigating the forces and fatigue of the strut to blade connection, would greatly improve the performance of VAWT wind turbines and make them more reliable.
Vertical axis wind turbines blade designs often comprise a hollow blade, which surrounds a central I-beam. The I-beam is typically made of a rigid material such as metal and provides the rigid backbone of the turbine blade and it comprises connection elements so that support struts can be firmly attached to the blade. The introduction of a rigid and often quiet heavy I-beam into the blade structure has very detrimental effects on the performance of the blade. Any method, which can avoid the need for a separate I-beam with additional fixings within the blade structure and one which keeps a more uniform weight distribution of the blade as well as keeping the blade as light as possible is highly desirable.
Generally, VAWT struts introduce drag and lower the performance of the wind turbine at any wind speed. An optimum design would also include aerodynamic profiles, which provide lift at every point of the support strut systems and which can be curvilinear adapted where needed and have a differential profile along the length of the strut.
Vertical axis wind turbines would also greatly benefit from a method to enable the wind turbine blade to accommodate the forces on the blade and strut, which change from compressional to tensional once per cycle as the blade turns into and out of the wind. The capability of the blade and strut to move would offer the means to smooth the torque over a wider part of the cycle and thus reduce fatigue upon the power transfer components to which the support strut is connected.
Conventionally wind turbines are designed to maintain the difference between the speed of the blade and the speed of the wind, otherwise known as the tip speed ratio to around 3. This ratio is maintained by the power control electronics such that power is taken off as the wind speed increases and less power is taken off as the wind speed reduces. Essentially the ability of the control algorithm to keep the tip speed ratio to its design value translates to a measure of the power efficiency of the wind turbine. The disadvantage of using a low tip speed ratio such as 3 is that the wind turbine has a corresponding narrower peak efficiency than a turbine with a higher tip speed ratio and it is harder to maintain the power output efficiency of the wind turbine when the wind speeds are changing. The peak efficiency of a wind turbine using a control algorithm, which only takes power off at a higher tip speed ratio results in higher performance because the peak efficiency is high over a wider range of wind speeds. Should the wind speed drop, a wind turbine which incorporates a power control algorithm which takes off power at a higher tip speed ratio results in a power generation efficiency which does not drop so fast as a wind turbine designed to generate power at a lower tip speed ratio. A VAWT wind turbine design, which is capable of addressing this performance deficiency, is greatly needed.
A further problem of wind turbines in general is that detailed knowledge of the integrity of the blade structure and any change in performance due to fatigue, which may occur over time, is not readily obtained. If it were possible to incorporate an intelligent strain gauge into the blade and or strut and to gather data from this strain gauge in real time, detailed knowledge of the integrity of the blade and strut as a function of cycle and as a function of time could be determined.
It is towards the creation of a new, lightweight, robust, cheaper and higher performance VAWT wind turbine design that the current invention is directed.
No systems are presently known to the applicants, which address this market need in a highly effective and economic way.
Further to the limitations of existing technologies used for designs for VAWT wind turbines, and so far as is known, no optimised system and method for a vertical axis wind turbine is presently available which is directed towards the specific needs of this problem area as outlined.